Abstract EANA2025-134

Space exposure experiments have gathered essential data about the resistance of terrestrial microorganisms to solar radiation outside of the Earth’s atmosphere, and the effects of such radiation on biomolecules pertinent to investigations of the origins of life and biosignature detection. Many past space exposure experiments have utilised space-based platforms to successfully study the limits of survival of microorganisms and the stability of macromolecules exposed to solar radiation in LEO, based on post-flight analyses in ground-based facilities. With the programmed end of the research activities on the ISS approaching, the astrobiology community is preparing for future activities in LEO and Beyond, including future research platforms on the Moon and in lunar orbit. For this, preparations must be made to continue exposure experiments using alternative platforms, and without a strict requirement for samples to be returned to ground-based facilities for analyses. Instruments and baseline data are needed for in situ space measurements [1].

Exocube (Exposure of organics/organisms cube) is part of a new generation of space exposure experiments that monitor experimental parameters in-situ via spectroscopic instrumentation. Led by project PI Dr Andreas Elsaesser, the Exocube project aims to gain insights into the biological and photochemical stability of life’s building blocks. Exocube is currently being developed by ESA for Exobio1 (Bartelomeo exposure platform outside the ISS Columbus module, 2026-2027). Exocube leverages existing cubesat technology from the O/OREOS satellite [2] and other space exposure platforms [3-4] pushing forward the design and development of in-situ astrobiology through use of a miniaturized Fourier transform infrared spectrometer and a system of LEDs and photodiodes for colorimetric and fluorescent spectrophotometry. Exocube will expose both living organisms and organic bio-marker molecules to cosmic and solar radiation. In addition to developing in situ hardware for space-based astrobiology, the data obtained will contribute to the growing catalogue of space exposure data for use in interpretating the results of past and upcoming planetary exploration missions.

As part of the international Exocube science team, our group focuses on salt-loving (halophilic) microorganisms and preservation of their cell envelope as biosignatures.  Evidence for past and present high salinity conditions are found throughout the solar system, from Enceladus and Europa, to Mars and in meteorites [5-7]. Evaporite crystals are known to be UV-shielding [8], and organics have been preserved within the brine inclusions of extraterrestrial halite (NaCl) crystals [9] demonstrating their preservation potential. The survival of halophilic archaea has previously been measured after exposed to space conditions on Biopan1-3, EXPOSE-E/-R/-R2, as well as ground simulations of Martian conditions as well as high-energy heavy ions and ionizing radiation [10–12]. The survival limits and associated molecular mechanisms of the halophilic archaeon Halobacterium salinarum have already been ascertained for exposure to desiccation, high vacuum, UV-C, and gamma irradiation [13-16]. We have recently detailed the mechanisms for H. salinarum surviving entrapment within halite fluid inclusions [17], fluorescent markers of haloarchaea cell activity [18], and biochemical preservation of dead cell envelopes in Mars and Earth relevant brines [19-21]. The objective of the Exocube halophile (ExocubeHALO) project is to evaluate in situ the effects of full-spectrum solar irradiation in LEO on the preservation of the cell envelopes of haloarchaea entombed within halite. This will expand our knowledge of halophilic biosignatures and potential survival with relevant to astrobiological exploration of the solar system.

 

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[21]Bourmancé, L. et al. Int J Astrobiol (2025). Accepted